Southern Pacific class MC-4
's MC-4 class of steam locomotive was the second class ordered and built as cab forward locomotives. Southern Pacific found the MC-2 class sufficient for a proof-of-concept for cab forward locomotives and sought to continue with now tested designs.
In service, SP found that the locomotives were a little too slow for the traffic needs. By 1930, all of the MC-4 class had been "simpled" to use uniform size cylinders and feedwater heaters were installed to address the issue. They were then reclassified as AC-2 locomotives. As rebuilt, the locomotives continued in service through the end of World War II.
